Spark excited oscillator



United States Patent SPARK EXCITED OSCILLATOR Milton G. White, Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application January 15, 1946, Serial No. 641,340

10 Claims. (Cl. 250-36) My invention relates broadly to ultra high frequency oscillators and more specifically to a novel type of selfpulsing oscillator in which energy is stored 1n the capacitance of a high Q resonant cavity and periodically discharged, oscillations being developed in the cavity during the discharge by the interchange of energy between the electric magnetic fields therein.

One object of my invention is to provide means for generating, within a resonant cavity, pulses of ultra high frequency energy of considerable power.

Another object of my invention is to provide an 1nherently stable ultra high frequency oscillator which will generate pulses of energy at a frequency which is primarily determined by the physical dimensions of the oscillator structure.

Another object of my invention is to provide an ultra high frequency oscillator which will generate pulses of energy at a repetition rate which may be made variable if desired.

Still another object of my invention is to provide means whereby the frequencies generated within the oscillator may be readily coupled to an external load or transmission line for utilization in any manner desired.

The above and other objects of my invention will be more apparent to those skilled in the art from a consideration of the detailed description which follows taken together with the accompanying drawings, in wh1ch;

Fig. 1 shows a cross section view of one embodiment of my invention;

Fig. 2 is a schematic representation of the equivalent electrical circuit of the embodiment of Fig. 1 when pulses of oscillations are being generated therein;

Fig. 3 is a schematic representation of the equivalent electrical charging circuit of the embodiment of Fig. 1 which exists during the intervals between pulses of oscillations; and

Fig. 4 shows a partial cross section view of a second embodiment of my invention.

Referring to Fig. 1, the embodiment of my invention shown consists of two similar conducting rings 1 and 6, ring 1 being formed in such a manner as to have an outwardly extending flange 3 at one end and an inwardly extending flange 2 at the other, ring 6 being similarly formed with outwardly extending flange 5 and inwardly extending flange 8. A dielectric ring 4, preferably composed of mica or some other material possessing high dielectric constant and insulating properties separates the outwardly extending flanges 3 and 5, whose faces are addressed one to the other, and provides electrical insulation and capacitance therebetween. The purpose of the dielectric ring and flange arrangement is to increase the capacitance between flanged rings 1 and 6. As will be seen from the drawing, flanged rings 1 and 6 abut opposite faces of dielectric ring 4 in a manner to form a partially enclosed cylindrical chamber. Provision is made, as at 17, for connecting ring 1 through an external variable resistance 18 to a source of positive D. C. voltage at terminal 19, While ring 6 is held at ground potential, as at 20. The bases of two conducting electrodes 13 and 15, of substantially funnel-like shape, are electrically and mechanically joined as at 16, to inwardly extending flanges 2 and 8 respectively in such a manner as to form an enclosed resonant cavity composed of substantially similar upper and lower halves having electrical capacitance and insulation therebetween. The resonant frequency of the cavity will be primarily determined by its physical dimensions. The smaller ends of discharge "ice electrodes 13 and 15 extend inwardly toward the center of the cavity and are separated by a distance whose value will largely determine the breakdown characteristics of discharge gap 14 formed therebetween. A hermetically sealed envelope 9, of insulating material such as glass, seals discharge electrodes 13 and 15 including discharge gap 14 in a region of gas or water vapor. The pressure and type of gas or water vapor employed will be largely determined by the breakdown characteristics of discharge gap 14 and upon the rapidity of breakdown obtainable thereby. In order to generate oscillations within the cavity, it is necessary that almost immediate breakdown of discharge gap 14 take place upon the application of the characteristic breakdown or firing potential between discharge electrodes 13 and 15. In order for this to occur, there must be present in discharge gap 14 at least one free electron or ionized particle which will produce further ions by collision with other molecules of gas. An auxiliary electrode 11 may be employed to aid in the rapid breakdown of discharge gap 14 by insuring the presence of such free ions within the gap.

Electrode 11 may be supported near the smaller end of and within hollow discharge electrode 15 as shown. A negative D. C. voltage is applied to the electrode 11, as at terminal 10, of magnitude suflicient to maintain a steady glow discharge between auxiliary electrode 11 and the inside of discharge electrode 15. Occasional free ions from the steady discharge so induced will migrate into discharge gap 14. As a still further precaution to insure the presence of free ions within discharge gap 14, auxiliary electrode 11 may be coated with a thin covering 12 of radioactive material. Emanations from this material will cause further occasional ions to appear within discharge gap 14 to further insure its rapid breakdown upon application of the firing potential.

The pulses of energy generated within the cavity by the periodic firing of discharge gap 14, as will be next described, may be coupled to an external load or transmission line by means of a conventional coupling loop 7, well-known in the art, which extends within and is electrically joined to the inside of the cavity.

The operation of the embodiment of Fig. l is as follows:

Upon the application of a source of positive D. C. voltage at terminal 19 the capacitance between the upper and lower halves of the cavity will begin to charge, drawing a charging current which will pass through external resistance 18 in series with the capacitance to ground. The equivalent D. C. charging circuit at this instant of time may be schematically represented as shown in Fig. 3 where E represents the applied D. C. voltage, R the external resistance, C the capacitance between the upper and lower halves of the cavity, and i the charging current. As the capacitance of the cavity charges, the voltage between the upper and lower halves of the cavity and hence between discharge electrodes 13 and 15 will rise along the conventional exponential curve.

The capacitance of the cavity will continue to charge until the voltage difference between electrodes 13 and 15 reaches the firing potential of discharge gap 14, when the gap will fire, discharging the electrostatic energy stored in the capacitance during the charging period. The discharge across gap 14 will excite oscillations within the cavity in its resonant mode by the interchange of energy between the electric and magnetic fields therein. The schematic circuit of Fig. 2 is approximately equivalent to the cavity of Fig. 1 while the discharge is occurring. In Fig. 2, R, C, Li and L2 represent external resistance 18, the capacity and inductance of the cavity, and the inductance of coupling loop 7 respectively of Fig. 1, and M the mutual inductance between L1 and L2. The firing of discharge gap 14 switches the inductance L1 of the cavity in series with the capacitance C, and the inductance and capacitance will resonate at a frequency determined by the magnitude of each and the losses of and output from the cavity. Similar oscillations will be induced in coupling loop 7, which may be connected to an external load or transmission line as above-described. After a short interval, the oscillations within the cavity will be reduced through attenuation and dissipation of energy and the potential across discharge gap 14 will drop below the critical extinguishing potential, causing the discharge to cease. The capacitance between the two halves of the cavity will then begin to charge as before until the critical firing potential across discharge gap 14 is again reached, causing the gap to discharge and produce another similar pulse of oscillations.

It may readily be shown upon further development of the conventional equation for the charging of a capacitance that the charging time between pulses will be:

150 RC log when ta -charging time in seconds between pulses of oscillation R=resistance in ohms of external resistance 18 C=capacity in farads between the upper and lower halves of the cavity E=applied D. C. potential at 19 in volts Ve=cri1tilcal extinguishing potential in volts of discharge Vi=critical firing potential in volts of discharge gap 14 Examination of the above equation will show that the time interval between successive pulses is directly proportional to the value of external resistance 18 and that the repetition rate may be readily controlled by varia tion of resistance 18. This resistor is hence made variable for control of the repetition rate or frequency.

Fig. 4 shows a second embodiment of my invention,

consisting of a resonant cavity substantially similar to that of Fig. 1 but employing a vibrating mechanical rather than a gaseous switch for periodic discharging of the capacitance between the upper and lower cavity halves.

Referring now in greater detail to the embodiment of Fig. 4, the components not shown or only partially shown thereon are similar to those of the embodiment of Fig. 1. A hollow cylindrical structure 32, composed of conducting material such as copper, is supported within the cavity by means of an outwardly extending flange 26 formed on one end, electrically and mechanically joined to inwardly extending flange 21, as at 22, of the upper cavity ring (not shown). A second and similar structure 37 is similarly supported by means of flange 40 similarly electrically and mechanically joined to inwardly extending flange 39 of the lower cavity ring (not shown). Structures 32 and 37 are positioned in such a manner that their unflanged ends extend inwardly towards the center of the cavity and are separated one from the other by a suitable distance. Circular flexible diaphragms 33 and 36, composed of conducting material, of diameters substantially the same as those of structures 32 and 37, are abutted over the unflanged ends of structures 32 and 37 respectively, being electrically and mechanically joined thereto by any suitable means. Rods 31 and 38, of conducting magnetic material, extend coaxially through structures 32 and 37 respectively, additionally extending through and being electrically and mechanically joined to openings of appropriate size formed in the centers of diaphragms 33 and 36 respectively. Electric contacts 34 and 35, composed of suitable material such as tungsten, are electrically and mechanically joined to the inwardly extending ends of rods 31 and 38 respectively. Rods 31 and 38 are additionally positioned along a common longitudinal axis in such a manner that inward flexing of diaphragms 33 and 36 will cause contacts 34 and 35 to be brought in electric contact one to the other. Electric solenoid coils 25 and 41 are supported, by any suitable means, about the respective outwardly extending ends of rods 31 and 38 in such a manner that rods 31 and 38 will act as movable magnetic cores for solenoid coils 25 and 41 respectively. A hermetically sealed envelope 30, of insulating material such as glass, seals structures 32 and 37, contacts 34 and 35, rods 31 and 38, and solenoid coils 25 and 41, in a common evacuated region. Provision is made at terminals 23 and 24 for the application to solenoid coils 25 and 41, whose windings are suitably phased, of a fluctuating voltage from an external source (not shown), such as an audio oscillator, of suitable frequency and magnitude so as to cause contacts 34 and 35 to alternately open and close at any desired repetition rate.

The operation of the embodiment of Fig. 4 is as follows: Solenoids 25 and 41 will be excited by the voltage applied to terminals 23 and 24 in such a manner as to cause rods 31 and 38 to simultaneously move alternately inwardly and outwardly toward the center of the cavity thereby causing contacts 34 and 35 to alternately close and open one to the other. The repetition rate of the opening and closing of contacts 34 and 35 will be determined by the frequency of the voltage source applied to terminals 23 and 24, which may be made variable if desired.

During the interval that contacts 34 and 35 are open, a charging current will flow from a source of D. C. voltage applied at terminal 29 through external resistance 28 and the capacitance between the upper and lower halves of the cavity to ground, as at 42, charging the capacitance between the cavity halves. As contacts 34 and 35 close, the charged capacitance will discharge therethrough, exciting a pulse of oscillations within the cavity in a manner similar to that of the embodiment of Fig. 1. The above described charging and discharging action is repetitive, thereby causing a series of pulses of ultra high frequency oscillations to be generated within the cavity whose frequency will be primarily determined by the physical dimensions of the cavity and whose repetition rate will be determined by the repetition rate of alternate opening and closing of contacts 34 and 35.

Various modifications and arrangements which may be made without departing from the spirit of the principles above-described will be apparent to those skilled in the art. My invention is only to be limited by the appended claims.

I claim:

1. An oscillator for the generation of pulses of ultra high frequency energy comprising, a first and second conducting ring each being substantially similar in form and flanged in such a manner as to have an outwardly extending flange at one end and an inwardly extending flange at the other end, a dielectric ring supported between the abutting faces of said outwardly extending flanges providing electrical insulation and capacitance therebetween, a partially enclosed chamber of substantially cylindrical shape formed by said rings and said inwardly extending flanges, 21 first and second similar conducting discharge electrode of substantially funnel-like shape positioned with the smaller ends of said electrodes extending inwardly towards the center of said chamber and separated by a predetermined discharge gap, the bases of said first and second electrodes being electrically and mechanically joined to said inwardly extending flanges of said first and second ring respectively in such a manner as to form a resonant cavity, a hermetically sealed envelope containing a gas of predetermined characteristics and pressure concentrically disposed about and sealing said discharge gap and electrodes from the surrounding atmosphere, a variable external resistance, means for electrically connecting one end of said resistance to said first ring, means for applying a source of high direct voltage to the other end of said resistance, means for maintaining said second ring at ground potential, and a coupling loop extending within and electrically joined to said cavity, whereby said source of high direct voltage will cause a charging current to flow through said external resistance and said capacitance to said grounded ring, periodically charging said capacitance to a potential sufiicient to cause the discharge of said capacitance across said discharge gap, thereby exciting periodic pulses of oscillations within said cavity at a frequency determined primarily by the physical dimensions of said cavity, the repetition rate of said pulses being controllable by said external resistance.

2. In combination with claim 1, a third electrode supported within said envelope near the smaller end of said second discharge electrode, means for applying a negative direct potential to said third electrode of a magnitude sufficient to induce a continuous glow discharge between said third electrode and said second discharge electrode, in order to provide a sufficient number of free ions within said discharge gap to permit immediate breakdown of said discharge gap upon the application of the critical firing potential thereacross.

3. An oscillator for the generation of pulses of ultra high frequency energy comprising, a resonant cavity composed of a first and second substantially similar cupshaped section of conducting material, means for electrically insulating said sections one from the other and providing electrical capacitance therebetween, an external resistance, means for connecting one end of said resistance to said first section, means for applying a direct potential to the other end of said resistance, means for maintaining said second section at ground potential, a first and second electric contact mechanically supported within said cavity, said first contact being electrically connected to said first section and insulated from said second section and said second contact being electrically connected to said second section and insulated from said first section, means for enclosing said contacts in a common evacuated region, means for causing said contacts to alternately open and close one to the other at any desired repetition rate in such a manner as to periodically electrically connect said first section to said second section, whereby there will be generated within said cavity periodic pulses of oscillations at a frequency determined primarily by the physical dimensions of said cavity and at a repetition rate determined by said repetition rate of said alternate opening and closing of said contacts one to the other, and means for coupling said pulses of oscillations generated within said cavity to an external load.

4. An oscillator for the generation of pulses of ultrahigh frequency energy comprising, a cavity resonator composed of first and second substantially similar cupshaped sections of conducting material, means for electrically insulating said sections one from the other and forming an electrical capacitance therewith, a source of direct current, an electrical resistor, a gas discharge tube connected to shunt said capacitance, means for charging said capacitance from said source through said resistor to a potential sufficient to cause conduction of said gas discharge tube thereby discharging said capacitance into the inductance of said resonator to excite ultra-high frequency oscillations in the resonant mode of said resonator by the interchange of energy between the electric and magnetic field therein until the potential across said gas discharge tube falls below the critical extinguishing potential of said tube and conduction of said tube terminates.

5. An oscillator for the generation of pulses of ultrahigh frequency energy comprising, a cavity resonator composed of first and second substantially similar cupshaped sections of conducting material, means for electrically insulating said sections one from the other and forming an electrical capacitance therewith, a source of direct current, an electrical resistor, a gas discharge tube connected to shunt said capacitance, means for charging said capacitance from said source through said resistor to a potential sufficient to cause conduction of said gas discharge tube thereby discharging said capacitance into the inductance of said resonator to excite ultra-high frequency oscillations in the resonant mode of said resonator by the interchange of energy between the electric and magnetic field therein until the potential across said gas discharge tube falls below the critical extinguishing potential of said tube and conduction of said tube terminates, and means for adjusting said resistor to control the rate of charge of said capacitance to control the time interval between the successive period of conduction of said gas discharge tube.

6. In an oscillator for the generation of pulses of ultrahigh frequency of the type comprising, a cavity resonator having first and second conductive sections spaced by a dielectric section to form an electrical capacitance, the combination comprising first and second electrodes mechanically and electrically connected to said first and second conductive sections, respectively, and separated from each other by a discharge gap, and means hermetically isolating said electrodes in the region of said gap from the surrounding atmosphere within said cavity resonator.

7. In an oscillator for the generation of pulses of ultrahigh frequency energy comprising, a cavity resonator having first and second conductive sections spaced by a dielectric section to form an electrical capacitance, the combination comprising first and second electrodes mechanically and electrically connected to said first and second conductive sections, respectively, and separated from each other by a discharge gap, means hermetically isolating said electrodes in the region of said gap from the surrounding atmosphere within said cavity resonator, a source of direct current, means for charging said capacitance from said source, means for regulating the rate of charge, means for facilitating periodic discharge of said capacitance through said electrodes to thereby generate ultrahigh frequency oscillations Within said cavity resonator, and means extending within said cavity resonator for coupling the pulses of oscillations resulting from said periodic discharge of said capacitance to an external load.

8. An oscillator of the type described in claim 7 wherein the electrodes are fixedly positioned along a common axis and said means for facilitating periodic discharge of said capacitance comprises an ionizable gas surrounding said electrodes.

9. In an oscillator for. the generation of pulses of ultrahigh frequency of the type comprising, a cavity resonator having first and second conductive sections spaced by a dielectric section to form an electrical capacitance, the combination comprising first and second electrodes mechanically and electrically connected to said first and second conductive sections, respectively, means for hermetically isolating said electrodes from the surrounding atmosphere within said cavity resonator, means for charging the capacitance of said cavity resonator from a source of direct current, and means for periodically discharging said capacitance through said electrodes to excite pulses of oscillations within said cavity during said discharge period, and means for regulating the rate of charge of said capacitance to control the time interval between successive pulses of oscillations.

10. An oscillator of the type described in claim 9 including means for causing said electrodes alternately to move toward and away from each other at any desired repetition rate in such a manner as periodically to contact each other and thereby periodically to connect electrically said first conductive section to said second conductive section.

References Cited in the file of this patent UNITED STATES PATENTS 1,407,061 Gray Feb. 21, 1922 2,205,852 Hollmann June 25, 1940 2,244,747 Varian et a1. June 10, 1941 2,408,405 Beniofi Oct. 1, 1946 2,534,098 Apker et a1 Dec. 12, 1950 OTHER REFERENCES Ser. No. 297,656, Jaumann (A. P. C.), published May 18, 1943. 

